Underneath Surface Alignment System for Step and Repeat Exposures
Original Publication Date: 1978-Jun-01
Included in the Prior Art Database: 2005-Feb-21
Up to now, the alignment in step and repeat optical projection has been obtained on the front surface of the wafer and has required looking through a layer of resist. Subsequent photolithographic steps made the visibility of alignment marks worse. If new alignment aids were added, the total error would increase.